This invention concerns a process for producing high-molecular weight linear alpha-olefins by catalytic dimerization of low molecular weight linear alpha-olefins. In particular, the process uses a catalyst prepared by complexing bis(1,5-cyclooctadiene) nickel( 0) and hexafluoro-2,4-pentanedione. The product olefins, particularly the intermediate weight range olefins, are used to prepare biodegradable detergents. For instance, such olefins can be reacted with sulfur trioxide to prepare alpha-olefin sulfonates. Alternatively, the olefins can be converted to the corresponding alcohol using the "oxo" process or sulfuric acid catalyzed hydration. The alcohol can be ethoxylated with ethylene oxide to form conventional detergent compounds.
A variety of catalysts have been proposed for use in dimerization or oligomerization processes. U.S. Pat. No. 3,676,523, granted July 11, 1972, discloses ethylene growth catalysts prepared using divalent nickel salts, a reducing agent and an o-dihydrocarbylphosphinobenzoate ligand. U.S. Pat. No. 3,825,615, granted July 23, 1974, discloses catalysts prepared using divalent nickel salts, a reducing agent and dicyclohexylphosphinopropionic acid or a salt thereof.
Catalysts comprising zero-valent nickel compounds have also been used in ethylene oligomerization processes. For instance, U.S. Pat. No. 3,644,563 discloses a process for oligimerizing ethylene which employs a catalyst comprising a nickel chelate of a bidentate ligand having a tertiary organophosphorus moiety and a carboxymethyl or carboxyethyl group attached directly to the phosphorus atom of the organophosphorus moiety and an inorganic siliceous oxide support. U.S. Pat. No. 3,644,564 discloses an ethylene oligomerization process using a catalyst which is the product of the reaction of a nickel compound which is an atom of nickel in complex with an olefinically unsaturated compound with a fluorine-containing ligand. The preferred nickel compound is bis(1,5-cyclooctadiene) nickel(0). The fluorine-containing ligands are selected from the group consisting of trifluoroacetic acid, 4,4,4-trifluoro-3-hydroxy-3-trifluoromethylbutyric acid, perfluoro-propene, hexafluoro, acetylacetone and trifluoroacetylacetone. Catalyst systems for dimerizing 1-olefins have also been suggested in the art. For instance, J. R. Jones, Journal of Chemical Society (C), 1124 (1971) discusses the dimerization of propene and other 1-olefins with a homogenous catalyst system comprising nickel acetylacetonate and diethylaluminum ethoxide.
Previously known processes which concern alpha-olefin dimerization, generally, produce a large proportion of polymer and a relatively small proportion of dimer. For instance, U.S. Pat. No. 3,825,615 describes the molecular weight distribution of typical products as conforming to a geometric distribution pattern expressed by the mathematical equation. EQU K = (C.sub.n +2)/(C.sub.n) (mols.)
That is, over the entire range of oligomers produced, the mol ratio of a given oligomer, Cn+2, over the one directly preceding it, Cn, remains essentially constant. In order to obtain attractive yields of detergent-range olefins, many processes attempt to control the ratio at about 0.9. This means that the amount of trimer produced according to typical oligomerization processes will approximate the amount of dimer. Where ethylene is the feed monomer, such a ratio is satisfactory. However, where propylene, hexene-1, or other alpha-olefins, besides ethylene, are used as feed olefins, it is especially advantageous to provide a process which produces substantial amounts of intermediate-weight-range dimer.
Moreover, it is important to produce "linear" alpha-olefins. The lineary of the product olefins is especially important where the product is intended for use in detergent manufacture. Thus, it is desirable to provide a catalyst system which not only provides an alpha-olefin dimer, but also provides a linear dimer.